Using the Xenonl33 inhalation technique, the regional cerebral blood flow (rCBF) lab within the Section on Clinical Neuropsychiatry, carries out investigations of rCBF (as an indicator of regional cortical metabolism) in a variety of neuropsychiatric patients and in normal subjects. Patient populations, including those with chronic schizophrenia, affective disorder, obsessive-compulsive disorder, Huntington's disease, Parkinson's disease, Alzheimer's disease, and dyslexia are studied before and during various exploratory and therapeutic interventions. Normal control subjects matched for each patient study are investigated concurrently. Cortical metabolic concomitants of states of normal cognition and consciousness are also being explored. The Xenonl33 method allows for multiple determinations of rCBF in a single individual who can, thus, serve as his or her own control while being studied serially under various cognitive and/or medication conditions. This allows paradigms to be designed to specifically test hypotheses about regional cortical function in disease states and normal higher cognitive function and to specifically monitor experimental and therapeutic interventions in neuropsychiatric disorders. Careful an creative application of this versative tool has produced important results. Experiments tailored to explore dorsolateral prefrontal cortex (DLPFC), and area of special interest in schizophrenia, have shown this area to be de-activated in patients with schizophrenia under conditions of cognitively specific, regionally selective demand of this area - conditions under which normals increase metabolism to DLPFC. In contrast Huntington's disease patients who are as cognitively impaired as schizophrenics, do not show DLPFC rCBF abnormality, but rather rCBF patterns similar to normal subjects. This is important evidence for the existence of subcortical dementia, which, until now, has been questioned by some.